The disclosure relates to a device for selectively regenerating and performing a tank leakage diagnosis of a tank ventilation system, especially of a motor vehicle, having a sorption filter for temporarily storing fuel evaporating from a fuel tank, and having a pump arranged on the fresh-air side of the sorption filter. The disclosure further relates to a method for selectively regenerating and performing a tank leakage diagnosis of a tank ventilation system and to a motor vehicle having a device according to the disclosure.
In a fuel tank of a motor vehicle, volatile substances such as hydrocarbons in the main and smaller fractions of other volatile constituents evaporate as a function of the pressure and temperature conditions prevailing in the tank, and a composition of the fuel. For environmental protection and safety reasons, these substances must be collected and fed to the engine for combustion. For this purpose the volatile substances are usually adsorbed by means of an activated charcoal filter and temporarily stored. For regeneration or desorption of the activated charcoal filter, the substances are extracted by means of a fluid flow—usually fresh air—and are fed to an intake pipe on the inlet side of the internal combustion engine for combustion. Here the extraction is achieved by means of a vacuum, which occurs in the intake pipe due to throttling of the engine.
In the case of turbocharged engines, hybrid vehicles and other engines in which the engine is operated as dethrottled as possible in order to reduce the fuel consumption, there is the fundamental problem that conventional tank ventilation does not adequately regenerate the activated charcoal filter by means of a vacuum in the intake pipe.
Statutory legislation in some countries furthermore demands testing of the functional efficiency of tank ventilation systems in motor vehicles by on-board means, that is to say a so-called on-board diagnosis (OBD). As part of the on-board diagnosis any leaks must be detected, signaled and corresponding data made available to an on-board memory for an off-board diagnosis to be performed in a workshop.
DE 101 31 162 A1 discloses a device for the leak-testing of a tank ventilation system of a motor vehicle, having an electrically operated pressure source, which by means of a switching valve can be selectively connected to the tank ventilation system and to at least one reference orifice. Here, when the tank ventilation system or the reference orifice is subjected to an excess pressure or a vacuum, an electrical variable or an electrical reference variable of the pressure source is detected. The variables are compared with one another and the existence of a leak from the tank ventilation system is inferred from the result of the comparison.
DE 197 35 549 A1 further discloses a device for the diagnosis of a tank ventilation system of a vehicle having a tank and an adsorption filter, which is connected to the tank by way of a tank connecting line. For ventilation the tank ventilation system comprises a tank ventilation valve, which is connected to the adsorption filter by way of a valve line. By means of an on-board pressure source a switch alternately subjects the tank ventilation system and a reference leak to a pressure and in this way detects any leakage. A shut-off device, which is opened to carry a flow when both the reference leak and the tank ventilation system is subjected to pressure, is provided between the on-board pressure source and the switch. The shut-off device, however, is arranged so that regeneration air does not flow through it, except during the diagnostic sequences, resulting in low level of contamination and an increased service life of the shut-off device. During the regeneration of the adsorption filter, the tank ventilation valve is opened, so that atmospheric air is drawn through the adsorption filter due to a vacuum prevailing in an intake pipe, thereby drawing the hydrocarbons that have accumulated in the adsorption filter into the intake pipe and feeding them to an internal combustion engine.
The object of the disclosure is to provide a device which is cost-effective to produce and which firstly allows improved regeneration or desorption of the sorption filter and secondly affords an on-board diagnosis of any leakage in the tank ventilation system.